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At least 91 records · Page 5Linked to original sources
PubMed2005

The analysis of interaural time differences in the chick brain stem.

The brain stem auditory system of the chick has proven to be a useful model system for analyzing how the brain encodes temporal information. This paper reviews some of the work on a circuit in the brain stem that compares the timing of information coming from the two ears to determine the location of a sound source. The contralateral projection from the cochlear nucleus, nucleus magnocellularis (NM), to nucleus laminaris (NL) forms a delay line as it proceeds from medial to lateral across NL. NL neurons function like coincidence detectors in that they respond maximally when input from the two ears arrive simultaneously. This arrangement may allow NL to code sound space by the relative level of activity across the nucleus. The head anatomy of the chick allows for enhancement of the functional interaural time differences. Comparing the functional interaural time differences to the length of the neural delay line suggests that each NL can encode approximately one hemifield of sound space. Finally it is suggested that inhibitory input into the NM-NL circuit may provide a means to dynamically adjust the gain of the circuit to allow accurate coding of sound location despite changes in overall sound intensity.

Acoustic Stimulation↗
PubMed1983

Computed tomography of the brain stem with intrathecal metrizamide. Part II: lesions in and around the brain stem.

The practical usefulness of computed tomography with intrathecal metrizamide in imaging the brain stem is illustrated in six examples where the lesions were misdiagnosed on intravenously enhanced computed tomography, angiography, or air study. Focal and diffuse atrophic changes of the brain stem were demonstrated in symptomatic patients where none of the other radiographic or clinical investigations were conclusive. Metrizamide computed tomography is probably the most sensitive method for imaging lesions in and around the brain stem and cerebellopontine angle.

Adolescent↗
PubMed1981

Frequency specificity of the auditory brain stem response.

Brain stem responses were obtained from eight young adult listeners with normal hearing. These potentials were evoked using three stimuli: a click, a 500 Hz, tone pip with a 2.5 ms. rise time, and a 500 Hz. tone pip with a 5.0 ms. rise time. Each stimulus was presented in quiet and in the presence of three high pass noises and one low pass noise. No significant difference in the latency-intensity function was obtained for the click between the quiet and the low pass noise conditions. There was, however, a significant prolongation of the latency in the presence of high pass noise. The latency of the brain stem response to the 500 Hz. tone pip was essentially unaffected by the high pass noise except for the 1200 Hz. high pass noise condition. These data indicated that for the tone pips a more basal region of the basilar membrane would be involved at high intensity stimulus levels. This involvement of basal regions, however, would not extend beyond the region responsive to a 2400 Hz. stimulus. The threshold for the click was significantly elevated in the high pass noise conditions but not in the low pass noise condition. The threshold of the 500 Hz. tone pip was significantly higher than that of the click in quiet and in the presence of noise.

Acoustic Stimulation↗
PubMed1980

Application of brain stem response in brain-injured children.

The early components of the auditory evoked potential within 10 msec following an auditory stimulus are attributed to the brain stem auditory nuclei and pathways. In pediatric neurology the auditory brain stem response (ABR) can be applied to: 1) differential diagnosis of hearing impairment in young children including objective threshold measurement of hearing, 2) electrophysiological evaluation of maturation of the auditory pathways, 3) diagnosis of the site and/or extent of neurlogical diseases affecting the brain stem and 4) observation of a degenerating process of degenerative diseases in the central nervous system. The paper is especially concerned with the application of ABR to severe neurological diseases in children including central auditory dysfunction, cerebral palsy, infantile spasm, adrenoleucodystrophy, anoxic brain damage and Down's syndrome. Value and limitation of ABR audiometry in the clinical practice were mentioned, and a special emphasis was placed on the fact that all types of auditory tests including behavioral, electrophysiological, and developmental tests are indispensable, because the ABR, like other indicators, also has its own limitation.

Brain Damage, Chronic↗
PubMed1984

Processing and analysis techniques for brain-stem auditory evoked potentials with localization of brain-stem lesions.

A computer assisted method of exact automatic measurement of BAEPs, mainly for the purpose of localization of brain-stem lesions, is described. The method presents analogue curves with superimposed confidence regions for the amplitudes and peak latencies of separate waves. The numerical output presents peak latencies, amplitudes, interpeak time intervals and central conduction times, all with normative values (60 healthy subjects), and +/- 2 and +/- 3 S.D. intervals and automatic labelling of pathological parameters (outside the chosen statistical limits). With the exception of the identification of separate waves in the often greatly distorted pathological BAEP the whole processing and display of the results are fully automatic.

Brain Diseases↗
PubMed2001

Brain stem PO(2) and pH of the working heart-brain stem preparation during vascular perfusion with aqueous medium.

The rat working heart-brain stem preparation (WHBP) is an in situ preparation having many of the advantages associated with in vitro preparations while retaining cardiovascular response functionality and an eupnoeic respiratory motor pattern. The preparation is perfused arterially with an aqueous medium having a much lower oxygen-carrying capacity than blood. To evaluate the efficacy of the artificial perfusion in providing adequate gas exchange within the brain stem, we used polarographic PO(2) and pH microelectrodes to determine the tissue PO(2) and pH of the medulla oblongata at various depths. When the perfusate was equilibrated with 5% CO(2) and 95% O(2), average tissue PO(2) was 294 Torr and no hypoxic areas were encountered. Tissue pH was remarkably uniform throughout the tissue, and on average was only 0.04 +/- 0.02 pH units more acidic than that of the perfusate. Increasing the PCO(2) of the perfusate increased tissue PO(2) and decreased arterial resistance. Decreasing perfusate PCO(2) (while keeping pH constant) decreased tissue PO(2) and reduced the respiratory activity. These results suggest that arterial PCO(2), independent of arterial pH, is an essential variable in determining both respiratory drive and cerebrovascular perfusion. We conclude that the medulla of the WHBP is oxygenated and within a physiological pH, which accounts for the eupneic pattern of respiratory motor activity it generates. Furthermore, this preparation may be a useful model for exploring mechanisms of central chemoreception as well as the dynamics of the cerebral vasculature responses following changes in blood gases.

Animals↗
PubMedDate not supplied

Reappearance of brain-stem auditory evoked potentials after surgical treatment of a brain-stem hemorrhage: contributions to the question of wave generation.

We report on a patient suffering a spontaneous hemorrhage primarily located in the right brain-stem; surgical correction of this led to a substantial improvement in clinical deficits. Brain-stem auditory evoked potentials (BAEPs) were recorded on postoperative days 18, 30, 55 and 205. Waves II through V were initially undetectable on stimulation of the damaged side, whereas the absence of peak V was the only abnormality seen on left-side stimulation. With the regression of the right lower mid-pontine deficits, the right waves gradually reappeared and normalized progressively. On the last recording, only a left wave V abnormality persisted. At that time, the patient had a moderate left hemisyndrome due to a circumscribed right upper pontine-midbrain lesion. Therefore, it can be suggested that the first 4 waves of BAEPs mainly originate in the ipsilateral pons, and the Vth in the contralateral higher regions.

Acoustic Stimulation↗
PubMed1981

[The clinical value of the orbicularis oculi reflex in combination with auditory evoked brain stem potentials in the diagnosis of disease processes in the cerebellopontile angle and brain stem].

The results of the Orbicularis oculi reflex (OOR) and the anditory evoked brain stem potential (a. e. BSP) supplement each other in the furnished information in lesions of the central and lower brain stem. The a. e. BSP permits quite a reliable localisation in the brain stem and in the cerebellopontile angle. the OOR moreover helps to discover disturbances in the N. facialis and the N. trigeminus. In intracanalicularly situated acousticus neurinomas lacking a. e. BSP the pathologically changed reflex response of the OOR indicates the process in the internal auditory canal.

Auditory Perception↗
PubMed1986

[Studies of brain stem function in infants with apnea syndrome using acoustically evoked brain stem potentials and heart rate variability].

Twenty-four infants aged between 6 days and 7 months and 2 infants (16 m and 3 y) were subjects of combined brain-stem auditory evoked potential and heart rate variability measurements. Ten infants had a sleep apnea syndrome and one a Near miss sudden infant death syndrome; thirteen infants formed the control group. Seventeen of the twenty-six infants had normal, age-depended brain stem potentials. All infants of the apnea syndrome-group, which had no therapy, had increased I to V interpeak latencies outside of the one-sigma level, the six infants treated with aminophylline were within the normal range. Heart rate variability measurements revealed the following mean +/- standard deviation of the control group: 4.5% +/- 1.5%; of the apnea syndrome-group without therapy: 5.4% +/- 2.0%.

Aminophylline↗
PubMed2005

Brain Stem Tumors.

Brain stem tumors are heterogeneous. They range from the diffuse pontine tumors, which are almost invariably fatal despite all known therapies, to lower-grade focal or exophytic tumors that often have a very good prognosis with surgery or observation only. In this article, we review the epidemiology of brain stem tumors and note that diffuse pontine tumors, although rare, are a significant contributor to mortality among pediatric oncology patients. Diagnosis in typical cases is made using a magnetic resonance imaging scan without biopsy. No highly effective standard treatment exists; therefore, inclusion of eligible patients in well-designed clinical research studies is extremely important. If an appropriate trial is not available, conventionally fractionated external beam radiation therapy can provide good short-term palliation to a significant proportion of patients. An important area of preclinical research that may soon be investigated in clinical trials for patients with diffuse pontine tumors is interstitial infusion of therapeutic agents, and the rationale for that approach is described in detail. Lastly, autopsy should be considered for patients who die of diffuse pontine tumors with the goal of obtaining tumor tissue for biological studies that may in the future lead to novel therapies.

Journal Article↗
PubMed1979

Bilaterally recorded brain stem auditory evoked responses. Their asymmetric abnormalities and lesions of the brain stem.

Simultaneous bilateral recordings (C3 to A1 and C4 to A2) of brain stem auditory evoked responses have been studied in 67 supratentorial lesions, nine midbrain lesions, 21 intrinsic pontine lesions, and 23 extrinsic compressions of the pons. The responses in supratentorial lesions showed completely normal records. In midbrain lesions, wave V was specifically altered. As wave 1 has been shown to be a far-field seventh nerve potential, and wave V the midbrain potential, waves II to IV can be inferred to originate in the central auditory pathway between the seventh nerve and the midbrain. Alterations of waves II to IV correlated well with localization of pontine lesions, and asymmetric alterations of the bilaterally recorded responses were associated with unilateral lesions of the brain stem auditory pathway and/or lesions of the crossed auditory projections.

Acoustic Stimulation↗
PubMed1996

Effects of brain stem lesions on cochlear function: mechanism of hearing improvement after removal of a brain stem tumor.

EOAEs are well correlated with changes of hearing sensitivity during the clinical course of brain stem lesions, as shown in this case study. They may serve as sensitive indicators to evaluate the possible effects of a brain stem lesion on cochlear function and monitor the attempted preservation of hearing during CPA or brain stem surgeries. It is thereby suggested that EOAEs should be included in an audiologic test battery in a differential diagnosis of retrocochlear lesions.

Audiometry, Pure-Tone↗
PubMed1986

Auditory brain stem responses and nonsense monosyllable perception test findings for patients with auditory nerve and brain stem lesions.

A nonsense monosyllable audiometric test was administered to 15 patients with eighth nerve or brain stem disorders caused by tumor, hemorrhage, encephalitis, and degenerative disease. Auditory brain stem responses (ABR) were abnormal in all patients. ABR abnormalities were defined by the absence of some or all waves or by prolongation of the wave V-I interval. The discrimination scores of the nonsense monosyllables were significantly lower in patients with completely absent ABR, with partial ABR series involving wave I, or with severely prolonged wave V-I intervals (over 3 SD). However, in patients with wave I only or with only moderately prolonged wave V-I intervals (less than 3 SD), test scores were within normal range. It is concluded that: 1. perception of nonsense monosyllables could be, though need not be, affected in patients with brain stem lesions; 2. eighth nerve lesions severely disrupt auditory comprehension as well as perception of nonsense monosyllables.

Adult↗
PubMed1989

Sequential changes of auditory brain stem responses in relation to intracranial and cerebral perfusion pressure and initiation of secondary brain stem damage.

The relationship of supratentorial intracranial pressure (ICP) and cerebral perfusion pressure (CCP) with serial changes in auditory evoked brain stem responses was investigated. Eighty-one patients without primary brain stem damage admitted to our emergency unit were studied. When ICP over 50 mm Hg persisted for 4 hours, the I-V interpeak latency was significantly prolonged. The threshold of this prolongation was 8 hours for the ICP over 45 mm Hg and 24 hours for that of over 40 mm Hg. The ICP of 35-40 mm Hg for 24 hours was the border zone. CCP did not show a significant relation with I-V interpeak latency changes. The loss of wave V was observed in a wide range of the ICP (30-147 mm Hg) and CPP (0-60 mm Hg). Wave III disappeared when the ICP exceeded 50 mm Hg. Wave I became undetectable with an ICP above 50 mm Hg or a CPP below 40 mm Hg. These results indicate that an increase of ICP over 40 mm Hg definitely initiates secondary brainstem dysfunction if it lasts for more than 24 hours and that the ICP should be reduced below this level, preferably below 35 mm Hg, to maintain brain function. The fact that both low CPP and high ICP were involved in the loss of wave I clearly shows that both ischaemia and displacement of the brain stem are the important pathophysiological factors for the disappearance of wave I.

Acoustic Stimulation↗